Rolling bearing, machine element, and solid-film formation method

ABSTRACT

A method is provided that forms a solid film on a bearing component of a rolling bearing. A solution containing a fluorine compound and a lubricant having no functional group is allowed to adhere to the bearing component as a liquid film, the fluorine compound containing 3-(trimethoxysilyl) propyl methacrylate, hexafluoropropene, and methyl methacrylate as components. The solid film is formed on the at least one of the bearing components by hardening the adhering liquid film.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2016-116115 filed onJun. 10, 2016 including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a rolling bearing, a machine element, and asolid-film formation method.

2. Description of the Related Art

When a rolling bearing is used in a vacuum environment or a corrosiveenvironment in which the use of grease or oil is precluded, bearingcomponents such as an inner ring and an outer ring are provided with afilm-like coating formed of a solid lubricant. The coating isconventionally formed of for example, soft metal such as gold, silver,or lead, or a layer structure material such as graphite or molybdenumdisulfide.

When the rolling bearing is provided with the coating formed of thesolid lubricant, a slight amount of solid lubricant peels off duringrotation of the bearing to contribute to lubrication. The use of thecoating reduces the number of dust particles from the rolling bearingcompared to the use of grease or oil. Nevertheless, in an environmentthat needs high cleanliness, the application of the coating poses aproblem. Thus, a rolling bearing has been proposed in which bearingcomponents are provided with a solid film of a fluorine-containingpolyurethane polymer compound (for example, Japanese Patent ApplicationPublication No. H9-137830 (JP H9-137830 A)).

The technique described in JP H9-137830 A provides a bearing that issuitable in a vacuum environment, a corrosive environment, and a cleanenvironment in which the use of grease or oil is precluded.

SUMMARY OF THE INVENTION

An object of the invention is to provide a rolling bearing and a machineelement that enable a reduction in the number of dust particlesgenerated and improvement of lubricity and a solid-film formation methodfor manufacturing the rolling bearing or the machine element.

The invention provides a rolling bearing including, as bearingcomponents, an inner ring, an outer ring, and a plurality of rollingelements interposed between the inner ring and the outer ring. At leastone of the bearing components is provided with a solid film of afluorine compound containing 3-(trimethoxysilyl) propyl methacrylate,hexafluoropropene, and methyl methacrylate as components. The solid filmcontains a lubricant dispersively added thereto and having no functionalgroup.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further features and advantages of the invention willbecome apparent from the following description of example embodimentswith reference to the accompanying drawings, wherein like numerals areused to represent like elements and wherein:

FIG. 1 is a sectional view depicting an embodiment of a rolling bearingin the invention;

FIG. 2 is a diagram depicting a general formula (chemical formula) of3-(trimethoxysilyl) propyl methacrylate;

FIG. 3 is a diagram depicting a general formula (chemical formula) ofhexafluoropropene;

FIG. 4 is a diagram depicting a general formula (chemical formula) ofmethyl methacrylate;

FIG. 5 is a diagram illustrating a solid film;

FIG. 6 is a diagram illustrating an apparatus for dust particle tests;

FIG. 7 is a diagram illustrating test conditions;

FIG. 8 is a graph illustrating the average number of dust particles(particles/cf) generated during 20 hours;

FIG. 9 is a graph illustrating periods until the time when the number ofdust particles exceeds a class 10 level (in other words, dust particlelife); and

FIG. 10 is a flow diagram illustrating a solid-film formation method.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a sectional view depicting an embodiment of a rolling bearingin the invention. A rolling bearing 10 includes an inner ring 11, anouter ring 12, a plurality of rolling elements 13, and a cage 14. In theembodiment depicted in FIG. 1, the rolling elements are balls 13. Inother words, the rolling bearing 10 is a ball bearing. A cage 14 is anannular member that holds the balls 13 at intervals in a circumferentialdirection. The inner ring 11, the outer ring 12, the balls 13, and thecage 14 are each referred to as a bearing component. In the presentembodiment, a solid film 15 is formed on a surface of each bearingcomponent.

The inner ring 11, the outer ring 12, the balls 13, and the cage 14 inthe present embodiment are formed of a material with corrosionresistance. The material with corrosion resistance may be, for example,martensitic stainless steel, austenitic stainless steel, or ceramicsmaterial. Instead of the corrosion-resistant material, carbon steel suchas bearing steel may be used to form inner ring 11, the outer ring 12,the balls 13, and the cage 14. The cage 14 may be formed of brass or asynthetic resin material.

The solid film 15 is formed all over the surface of each of the innerring 11, the outer ring 12, the balls 13, and the cage 14. The solidfilm 15 is formed of a fluorine compound containing 3-(trimethoxysilyl)propyl methacrylate, hexafluoropropene, and methyl methacrylate asmonomer components.

FIG. 2 depicts a general formula (chemical formula) illustrating thestructure of 3-(trimethoxysilyl) propyl methacrylate. FIG. 3 depicts ageneral formula (chemical formula) illustrating the structure ofhexafluoropropene. FIG. 4 depicts a general formula (chemical formula)illustrating the structure of methyl methacrylate.

The solid film 15 contains a lubricant dispersively added thereto andhaving no functional group such that the lubricant can flow out from thesolid film 15. The lubricant is a fluorine polymer, and in the presentembodiment, contains perfluoropolyether (also hereinafter referred to asPFPE oil). The solid film 15 contains the lubricant (fluorine polymer)that is dispersively added to the solid film and that is afluorine-based lubricant (fluorine-based lubricating oil) having nofunctional group. The solid film 15 is, for example, one to severalmaicrometers in thickness.

A formation method for the solid film 15 will be described. In theassembled state, the inner ring 11, the outer ring 12, the balls 13, andthe cage 14 have been degreased. In this regard, in the presentembodiment, the assembled rolling bearing 10 is degreased.

A solution described below is prepared, and the assembled rollingbearing 10 is immersed in the solution. The inner ring 11 and the outerring 12 are rotated several times relative to each other. Consequently,a liquid film (in other words, a film of the solution) can be allowed toadhere to the entire surface of each of the inner ring 11, the outerring 12, the balls 13, and the cage 14 (adhesion process).

The solution has a fluorine compound containing 3-(trimethoxysilyl)propyl methacrylate, hexafluoropropene, and methyl methacrylate asmonomer components, and further contains the lubricant(perfluoropolyether) that is a fluorine polymer. The fluorine compoundhas functional groups, whereas the lubricant has no functional group.The solution will further be described. A first solute refers to thefluorine compound containing 3-(trimethoxysilyl) propyl methacrylate,hexafluoropropene, and methyl methacrylate as monomer components. Asecond solute refers to perfluoropolyether (PFPE oil) having nofunctional group. The solution is prepared by diluting the firstsolution with a solvent and adding the second solute to a solutionresulting from the dilution. The solvent is a fluorine solvent,specifically, a mixture of ethyl nonafluoroisobutyl ether and ethylnonafluorobutylether.

In the solution, preferably, the first solute is 0.5 to 5 wt % inconcentration, whereas the second solute is 0.1 to 2 wt % inconcentration. When the first solute is less than 0.5 wt %, theresultant solid film 15 is a thin soft film, possibly leading to areduced friction resistance effect. When the first solute is more than 5wt % in concentration, the bearing components are firmly stuck togethervia the solid film 15. Then, unsticking the bearing components may bedifficult. Thus, the first solute is preferably 1 to 3 wt % inconcentration. When the second solute is less than 0.1 wt % inconcentration, the lubricant may produce a reduced lubrication effect.When the second solute is more than 2 wt % in concentration, theresultant solid film 15 may have low adhesion. Thus, the second soluteis more preferably 0.3 to 1 wt % in concentration.

Mixture of the first solute (the above-described fluorine compound) andthe second solute (perfluoropolyether) is preferably such that theamount of the first solute is larger than the amount of the secondsolute in order to provide the solid film 15 with the appropriateadhesiveness. That is, the mixture ratio between the first solute andthe second solute is preferably such that the first solute is higher inmixture rate than the second solute. For example, the mixture ratio ispreferably such that (first solute:second solute)=(4:1).

A solution resulting from the above-described mixture is allowed toadhere to the bearing components as a liquid film (adhesion step). Inthe description of the present embodiment, the rolling bearing 10 as awhole is immersed in the solution. However, any other technique may beused to allow the liquid film to adhere to the bearing components. Theliquid film may be allowed to adhere to the bearing components when thebearing components are separated from one another rather than after thebearing components are assembled together.

Then, the liquid film adhering to the bearing components is hardened. Aspecific method is to heat the rolling bearing 10 (hold the rollingbearing 10 in a thermostatic tank at 100° C. for 60 minutes) to allowthe film (liquid film) to undergo a hardening reaction. Consequently,the solid film 15 is formed on the surface of each of the bearingcomponents (film formation step). A temperature set for hardening of theliquid film may be 50° C. to 150° C. However, the temperature needs tobe equal to or lower than tempering temperatures of the bearingcomponents.

As described above, the solid-film formation method for forming thesolid film 15 on the bearing components of the rolling bearing 10includes the adhesion step and the film formation step as illustrated inFIG. 10. In the adhesion step, the solution is allowed to adhere to thebearing components as a liquid film, the solution containing thefluorine compound containing 3-(trimethoxysilyl) propyl methacrylate,hexafluoropropene, and methyl methacrylate as monomer components, andthe lubricant (PFPE oil) having no functional group. In the filmformation step, the adhering liquid film is hardened to form the solidfilm 15 on the bearing components.

The rolling bearing 10 manufactured by this method includes, as thebearing components, the inner ring 11, the outer ring 12, the balls 13interposed between the inner ring 11 and the outer ring 12, and the cage14. On the bearing components, the solid film 15 of the fluorinecompound is formed that contains 3-(trimethoxysilyl) propylmethacrylate, the hexafluoropropene, and methyl methacrylate as monomercomponents. The solid film 15 contains the lubricant of the fluorinepolymer that is dispersively added to the solid film 15 and that isflowable and has no functional group.

The resultant solid film 15 has a structure in which molecules are boundtogether as a result of the hardening reaction. In particular, asdepicted in FIG. 5, Si groups in the solid film 15 bind to hydroxylgroups (OH groups) in each bearing component (substrate M) to enhancethe adhesion of the solid film 15 to the bearing component. This enablesa reduction in the number of dust particles generated from the solidfilm 15. The bearing component generally has hydroxyl groups (OHgroups). The solid film 15 binds firmly to the bearing component due tosiloxane bonds and covers the surface of the bearing component. Thesolid film 15 is thus unlikely to be peeled off and enables a reductionin the number of dust particles generated. The left of FIG. 5illustrates a state before the hardening reaction, and the right of FIG.5 illustrates a state after the hardening reaction. The solid film 15contains the lubricant of the fluorine polymer dispersively added to thesolid film 15 so as to be flowable and having no functional group. Inother words, the lubricant of the fluorine polymer is flowable due tothe lack of functional groups. Consequently, the lubricant oozes throughthe solid film 15 to contribute to lubrication of the rolling bearing10, enabling enhancement of lubricity.

In the present embodiment, the lubricant is the fluorine polymer havingno functional group, thus enabling the lubrication performance of therolling bearing 10 to be improved. The fluorine compound (the firstsolute) has a higher mixture rate than the fluorine polymer (the secondsolute). This more effectively enhances the adhesion of the solid film15 to the bearing components. As described above, in the solid film 15in the present embodiment, the basic resin is a resin containingfluorine (the fluorine compound), to which the fluorine compound havingno functional group is added (instead of a conventional solidlubricant).

In the solid-film formation method in the present embodiment, thesolution used is prepared by adding the fluorine compound (the firstsolute) and the lubricant (the second solute, in other words,perfluoropolyether) to the solvent. The solvent is an ether containingat least one of ethyl nonafluoroisobutyl ether and ethylnonafluorobutylether. This eliminates the need for the use of two typesof solvents, that is, the solvent for the fluorine compound (for thefirst solute) and the solvent for the lubricant (for the second solute,in other words, perfluoropolyether).

Now, a dust particle life of the resultant solid film 15 will bedescribed. A first example and a first conventional example will bedescribed. In the first example, the assembled rolling bearing wasdegreased and washed, the solution was used to allow the liquid film toadhere to the rolling bearing (adhesion step), and the liquid film washardened (film formation step), as described in the embodiment. Therolling bearing was degreased and washed by using an ultrasonic washingmachine to perform washing in hexane for one minute and in acetone forone minute. The liquid film was allowed to adhere by immersing therolling bearing in the solution for one minute. The liquid film washardened by being baked at 100° C. for 60 minutes. In the first example,in the solution, the first solute (the fluorine compound) was 2 wt % inconcentration, the second solute (perfluoropolyether having nofunctional group) was 0.5 wt % in concentration, and the mixture ratioof the first solute to the second solute was 4:1. The first conventionalexample is a rolling bearing provided with a solid film offluorine-containing polyurethane polymer compound described inDescription of the Related Art (JP H9-137830 A).

The rolling bearings in the first example and the first conventionalexample were each attached to an apparatus depicted in FIG. 6, and dustparticle generation tests were conducted. Arrows in FIG. 6 indicateflows of air (clean air). The air flows through the bearing to aparticle counter. Test conditions are as follows.

FIG. 8 is a graph illustrating the average number of dust particles(particles/cf) generated during 20 hours since the start of the tests.

FIG. 9 is a graph illustrating periods until the time when the number ofdust particles exceeds a class 10 level (in other words, a dust particlelife). As depicted in FIG. 8, the average number of dust particles inthe first example is smaller than the average number of dust particlesin the first conventional example, and thus, the first example produceda preferable result. As depicted in FIG. 9, the dust particle life inthe first example is longer than the dust particle life in the firstconventional example, and thus, the first example produced a preferableresult.

As described above, in the rolling bearing 10 (first example) in thepresent embodiment, the solid film 15 adheres more appropriately to thebearing components, thus reducing the number of dust particles generatedfrom the solid film 15. The results of the tests (see FIG. 9) indicatethat the solid film 15 in the present embodiment can exhibit highdurability. The lubricant oozes through the solid film 15 to contributeto lubrication of the rolling bearing 10, allowing lubricity to beenhanced.

In the above-described embodiment, the inner ring 11, the outer ring 12,the balls 13, and the cage 14 are assembled together, and the assemblyis immersed in the solution to form the solid film 15. However, thebearing components in a separated state may be immersed in the solutionto form the solid film 15 on each of the bearing components before thebearing components are assembled together. In the description, the solidfilm 15 is formed on all of the inner ring 11, the outer ring 12, theballs 13, and the cage 14. The solid film 15 may be formed on at leastone of the bearing components. In this case, the solution may be allowedto adhere to at least one of the bearing components as the liquid film,and subsequently, the liquid film may be hardened. Then, the hearingcomponents may be assembled into the rolling bearing 10, that is, afinished product. Moreover, the rolling bearing 10 depicted in FIG. 1includes the cage 14. However, the invention may be applied to a rollingbearing from which the cage 14 is omitted.

The solid film 15 need not he formed all over each bearing component butmay cover a part of the bearing component. For example, for the innerring 11 and the outer ring 12, the solid film 15 may be formed on atleast a raceway surface contacted by the rolling elements (balls 13).When the cage 14 is in sliding contact with a part of the inner ring 11or the outer ring 12, the solid film 15 may be formed on that part.Alternatively, the solid film 15 may be formed exclusively on the(entire) surface of each of the rolling elements (balls 13) included inthe bearing components.

The solid-film formation method may be intended for machine elementsother than such a rolling bearing as depicted in FIG. 1. The solid filmmay be formed on components of such a machine element. The machineelement having the components on which the solid film is formed by thesolid-film formation method may be a linear motion element such as aball screw or a linear guide which includes components arranged inrolling contact with other components.

The embodiment disclosed above is illustrative in every way and is notrestrictive. In other words, the rolling bearing in the invention is notlimited to the illustrated form but may be in any other form within thescope of the invention.

The rolling bearing (machine element) in the invention allows the solidfilm to adhere more appropriately to the bearing components (components)to enable a reduction in the number of dust particles generated from thesolid film. The lubricant oozes through the solid film to allow forcontribution to lubrication of the rolling bearing (machine element),enabling lubricity to be enhanced. The solid-film formation method inthe invention enables the rolling bearing (machine element) as describedabove to be manufactured.

What is claimed is:
 1. A rolling bearing comprising, as bearingcomponents, an inner ring, an outer ring, and a plurality of rollingelements interposed between the inner ring and the outer ring, whereinat least one of the bearing components is provided with a solid film ofa fluorine compound containing 3-(trimethoxysilyl) propyl methacrylate,hexafluoropropene, and methyl methacrylate as components, and the solidfilm contains a lubricant dispersively added to the solid film andhaving no functional group.
 2. The rolling bearing according to claim 1,wherein the lubricant is a fluorine polymer.
 3. The rolling bearingaccording to claim 2, wherein the fluorine compound is higher in mixturerate than the fluorine polymer.
 4. A solid-film formation method forforming a solid film on at least one of bearing components of a rollingbearing including, as the bearing components, an inner ring, an outerring, and a plurality of rolling elements interposed between the innerring and the outer ring, the solid-film formation method comprising:allowing a solution containing a fluorine compound and a lubricanthaving no functional group to adhere to the at least one of the bearingcomponents as a liquid film, the fluorine compound containing3-(trimethoxysilyl) propyl methacrylate, hexafluoropropene, and methylmethacrylate as components; and forming the solid film on the at leastone of the bearing components by hardening the adhering liquid film. 5.The solid-film formation method according to claim 4, wherein thesolution is prepared by adding the fluorine compound and the lubricantto a solvent, the lubricant is perfluoropolyether, and the solvent is anether containing at least one of ethyl nonafluoroisobutyl ether andethyl nonafluorobutylether.
 6. A machine element comprising a componentmember that is rolling contact with another component member, whereinthe component member is provided with a solid film of a fluorinecompound containing 3-(trimethoxysilyl) propyl methacrylate,hexafluoropropene, and methyl methacrylate as components, and the solidfilm contains a lubricant dispersively added to the solid film andhaving no functional group.
 7. A solid-film formation method for forminga solid film on a component member of a machine element that is inrolling contact with another component member, the method comprising:allowing a solution containing a fluorine compound and a lubricanthaving no functional group to adhere to the component member as a liquidfilm, the fluorine compound containing 3-(trimethoxysilyl) propylmethacrylate, hexafluoropropene, and methyl methacrylate as components;and forming the solid film on the component member by hardening theadhering liquid film.
 8. The solid-film formation method according toclaim 4, wherein: a concentration of the fluorine compound in thesolution is in the range of 0.5 to 5 wt %, and a concentration of thelubricant in the solution is in the range of 0.1 to 2 wt %.
 9. Thesolid-film formation method according to claim 7, wherein: aconcentration of the fluorine compound in the solution is in the rangeof 0.5 to 5 wt %, and a concentration of the lubricant in the solutionis in the range of 0.1 to 2 wt %.